There are various types of conventional switching power supply apparatuses.
FIG. 14 is a circuit diagram showing a configuration of a switching power supply apparatus disclosed in Patent Literature (PTL) 1.
A switching power supply apparatus 900 controls on and off of a normally-on bidirectional switch 10 to directly convert AC voltage Vac of an AC source connected to a primary winding of a transformer into power of a secondary winding of the transformer and generate DC voltage.
The switching power supply apparatus 900 includes: the AC source; two gates G1 and G2; the normally-on bidirectional switch 10 controlled by the gates G1 and G2; a switch M1 which causes a short circuit between the gate G2 and a source S2 according to a control signal PWM; a switch M2 which causes a short circuit between the gate G1 and a source S1 according to a control signal PWM; a diode D2 which sets voltage of the gate G2 of the bidirectional switch 10 to be lower than that of the source S2 when the switch M1 is off; a resistance R1 which limits current of the diode D2; a diode D3 which sets voltage of the gate G1 of the bidirectional switch 10 to be lower than that of the source S1 when the switch M2 is off; a resistance R2 which limits current of the diode D3; transformers L1A and L1B each including a primary winding and a secondary winding; rectifier diodes D10 and D20; an inductance L40; a smoothing capacitance CL; and a load Z.
Hereinafter, a brief description will be given of an operation of the switching power supply apparatus 900.
When AC voltage Vac of the AC source is 0 V or above (positive voltage), the switch M2 is always set to be on, and the gate G1 and the source S1 of the bidirectional switch 10 are set to the same electric potential. On the other hand, the switch M1 is turned on and off according to the control signal PWM.
When the switch M1 is on, the gate G2 and the source S2 of the bidirectional switch 10 are set to the same potential, turning on the bidirectional switch 10. This causes a current flow in the primary winding of the transformer L1A, and current generated in the secondary winding is supplied to the inductance L40 and the smoothing capacitance CL via the rectifier diode D10. As a result, DC voltage is generated.
When the switch M1 is off, charges in the gate G2 of the bidirectional switch 10 are drawn via the diode D2 and the resistance R1, making the voltage of the gate G2 of the bidirectional switch 10 lower than that of the source S2. As a result, the bidirectional switch 10 is turned off. This interrupts current supply to the primary winding of the transformer L1A.
When AC voltage Vac of the AC source is less than 0 V (negative voltage), the switch M1 is always set to be on, and the gate G2 and the source S2 of the bidirectional switch 10 are set to the same potential. On the other hand, the switch M2 is turned on and off according to the control signal PWM. When the switch M2 is on, the gate G1 and the source S1 of the bidirectional switch 10 are set to the same potential, turning on the bidirectional switch 10. This causes a current flow in the primary winding of the transformer L1B, and current generated in the secondary winding is supplied to the inductance L40 and the smoothing capacitance CL via the rectifier diode D20. As a result, DC voltage is generated.
When the switch M2 is off, charges in the gate G1 of the bidirectional switch 10 are drawn via the diode D3 and the resistance R2, making the voltage of the gate G1 of the bidirectional switch 10 lower than that of the source S1. As a result, the bidirectional switch 10 is turned off. This interrupts current supply to the primary winding of the transformer L1B.
In accordance with above, the switching power supply apparatus 900 is capable of converting the AC voltage Vac of the AC source to power of the secondary windings of the transformers L1A and L1B, by controlling the gates G1 and G2 of the bidirectional switch 10. More specifically, it is possible to convert the AC voltage Vac of the AC source to power of the secondary windings of the transformer L1A and L1B without converting the AC voltage Vac of the AC source to DC current and voltage.